1. Field of the Invention
This invention relates generally to collapsible tubes used to contain and dispense fluids, and particularly to tubes having a seal of laminated material on the dispensing orifice of a prior art tube formed of a collapsible tube wall of laminate material welded to a plastic head portion.
Collapsible tubes are packages in tube form having a dispensing orifice at one end of a deformable tube. The tube is deformed and collapsed by squeezing so that the contents are forced out the orifice. Such tubes are used to contain toothpaste, pharmaceuticals, cosmetics, personal care products, artists' pigments, adhesives, sealants and caulking materials, greases and lubricants, foods and condiments, and many other products. Collapsible tubes generally have a screw cap closure.
2. Description of Related Art
a. Prior Art Collapsible Tubes
Collapsible tubes are formed of (1) metal alone or (2) plastic alone, or (3) a combination of a rigid plastic head portion and a deformable laminate tube body portion.
b. Method of Making Prior Art Collapsible Tubes
Metal tubes are formed by impact extrusion from metal slugs in a die cavity wherein a ram forces the metal into the tube shape.
Plastic tubes of, for instance, polyethylene, are injection molded into the desired tube shapes.
Laminate tubes consist of at least two parts; namely, (1) a rigid pure plastic head portion and (2) a tube body formed of a laminate of layers of plastic and metal foil, adhesively held together. The tube body is joined, in a separate step, to the molded plastic head by, for instance, radio frequency welding.
The tubes are filled through an open bottom. The tubes are then closed at the bottom, generally by a fold.
c. Prior Art Seals on Collapsible Tubes
Prior art collapsible tubes, particularly those formed of metal, often have a seal across the dispensing orifice of the tube. Seals are generally used when the tube contains medicinal products. The seal is pierced and deformed before the contents are discharged. An unbroken seal assures the user that the product has not been tampered with or otherwise contaminated. In use, the seal is pierced by, for instance, a point formed in the tube screw cap. It is highly desirable that the seal, once broken by the user, remains in a fixed, open position so that the contents can be easily squeezed from the tube.
Metal foil seals work extremely well, since they stay deformed, once pierced. Pure plastic seals are far less desirable since they spring back after being perforated and block the flow from the tube. Also, plastic tubes, in which plastic seals are easily formed, spring back after being squeezed and suck air back into the tube. The plastic tube does not stay deformed to shrink with the contents as does a metal tube.
Laminate tubes having rigid plastic heads welded to collapsible tube walls formed of a laminate of metal and plastic deform relatively well. Forming a seal of other than pure plastic, which is unsatisfactory on such tubes, however, is a problem. The tube dispensing orifice is in a head formed of a pure plastic, whereas the deformable tube body is made of a laminate which must be welded to the head portion having the dispensing orifice therein, in a separate step, to assemble the tube components.
d. Method of Forming Prior Art Seals
Prior art seals have been formed in different ways, depending upon the material from which the tube is made.
In a metal collapsible tube, a metal foil seal can be readily formed integral with the neck, across the mouth of the tube, by simply suitably designing the die cavity. The ram, in extruding the tube within the cavity, forms the integral metal seal. The seal is punctured prior to use and stays in its punctured position.
A seal can also be formed integral with the tube of pure plastic during the molding operation, wherein the entire tube is formed at one time. Plastic tubes lack the ability to shrink with the contents as the tube is used, since the springy plastic material holds its shape and sucks air into the package when hand pressure is removed. The plastic seal likewise is springy and does not retain its punctured condition, but rather springs back to block easy dispension of the contents.
Collapsible tubes called laminate tubes are formed of a laminate wall welded to a plastic head. The walls of such a tube do not spring back as do the pure plastic tubes. In contrast to metal tubes and pure plastic tubes which are formed in one piece in an extrusion or molding, laminate tubes are formed of individual parts assembled together. A head portion is injection molded of pure thermoplastic. A tube body of laminate is separately formed. The parts are then welded together. Since the head portions of the laminate tubes are of pure plastic and are molded, it is possible to mold a pure plastic seal in the mouth of the tube. As explained above, such pure plastic seal is unacceptable since, after piercing, it does not stay out of the way of discharge of the contents, but springs back to continue to form an obstacle across the mouth.
It is therefore necessary, in a laminate tube, to form a seal of a deformable material, such as a laminate, which can be welded to the laminate tube dispensing orifice in the head, which is formed of rigid plastic.
Problems arise in securing a seal of laminate to the dispensing orifice of the plastic head of a laminate tube in that the seal must be formed, positioned and held and then welded to the head as by heat sealing or radio frequency welding. In the prior art, as disclosed in U.S. Pat. No. 4,595,434, a seal of laminate material is secured to the dispensing orifice of a laminate tube after the laminate tube has been welded to the rigid plastic head portion. The seal of laminate is cut to the finished dimensions and placed within a screw cap closure of rigid plastic. The cap is then screwed on the neck of the tube over the dispensing orifice to hold the seal in position for welding by radio frequency. A ferrite mandrel is used within the tube to prevent damage to the weld between the wall and the head.
A problem with such method is that the seal cannot be visually inspected after completion without unscrewing the cap. A further problem is that the sealing operation takes place after the wall has been assembled to the head, so that extreme care must be taken that the shoulder weld between the rigid plastic head portion and the laminate wall portion is not damaged by the radio waves used to apply the seal. Additionally, it is cumbersome to cut and place a laminate seal in the head of a cap.
Considering that tubes are made on a mass basis with repetitive machine operations, these problems in the prior art represent a burden during the manufacturing process.
e. The U.S. Pat. No. 4,938,818
Prior art laminate tubes are formed of an injection molded solid thermoplastic head portion having an integral shoulder and neck, with a dispensing orifice therein, welded to a tube formed of a laminated wall. The wall has layers of metal foil, thermoplastic, and sometimes paper.
In the invention disclosed in U.S. Pat. No. 4,938,818, incorporated by reference herein, a seal of laminate material is cut, positioned on the head dispensing orifice and held thereto, and then heat-sealed by a hot press to the orifice before the head is welded to the laminate tube wall. When the tube wall is subsequently assembled and welded by radio frequency to the head, a special heat sink is positioned adjacent the seal to avoid damage to the seal.
The laminate material from which the seal is made is in web form and positioned across the head dispensing orifice. A seal is die cut from the web right over the orifice, whereupon it is held securely thereto by a vacuum applied through the bottom of the head through the orifice. A heat press is applied to the seal over the orifice and the thermoplastic layer in the seal laminate, which is adjacent to the thermoplastic lip of the dispensing orifice, melts the thermoplastic at the contact interface, after which the press is removed. The weld then cools, hardens, and fuses the seal to the outlet.
The head is then assembled with the tube wall, which has been preformed in prior art fashion. In forming the tube wall, a continuous web of material is formed into a continuous tube and then welded as by radio frequency along the longitudinal seam. The continuous tube so formed is then cut into lengths corresponding to the collapsible tube lengths.
The tube lengths are then assembled individually on a mandrel and brought into position adjacent the tube heads and welded thereto by radio frequency.
A special heat sink is placed adjacent the seal to absorb heat generated by the weld operation, so there is no heat buildup in the laminate seal, which contains a metal foil layer.
The seal of laminate material is pierced to gain access to the tube contents, as shown for instance by a cap having a point, as shown in FIG. 10 of the '818 patent.